The use of organic polyisocyanate, epoxy, urea formaldehyde (UF), and phenol formaldehyde resole resins (PF resins), and various combinations of these adhesives is well known for the production of consolidated wood composites such as chipboard, fiberboard, and related composite wood products as well as in making engineered lumber composites. The cure of these resins often is accelerated in these end-use applications by using heated presses with press temperatures exceeding 100° C., and often 200° C. In some specialized structural (or engineered) lumber applications it is often impractical to use heat to drive the cure of the adhesive because the engineered wood composite structures are too large for adequate heat transfer. In these structural applications, adhesives that cure at ambient temperatures are preferable. The challenge in formulating all of these resins is to achieve an adequate balance between the need for rapid cure at elevated or near-ambient temperatures, and to maintain a suitably long working time (or pot life).
Moreover, recent environmental concerns recognized the need for replacing UF and PF resins with more environmentally friendly resins that have the bond strength obtained with the UF resins, while eliminating formaldehyde and providing similar or better moisture resistance for the final product. Although polyisocyanates, for example, PMDI, are capable of providing these characteristics, to-date, many attempts to commercially use PMDI in replacing UF have failed due to cost and processing concerns.
There is still a need in the wood products industry for high performance, lower cost and environmentally cleaner adhesives that perform as well as polyisocyanates. Various attempts have been made to blend polyisocyanate adhesives with other kinds of adhesives but none have had significant commercial success in the certain industries, for example, the commodity wood products industry. The use of isocyanate-functional prepolymers has been extensively studied. Unfortunately, in many cases, the prepolymers simply dilute the performance of the isocyanate. It is, therefore, desirable to have a modifying agent or prepolymerizable species that can be combined with a polyisocyanate or another similar resin in order to reduce the cost of the latter by reducing the amount of polyisocyanate, which is needed without reducing performance such as bond strength and moisture resistance.